The proposed series of studies will examine the mechanisms underlying direction selectivity in the visual cortex and the effects of deprivation on the development and maintenance of these mechanisms. Iontophoretic application of neurotransmitters, specifically Gamma-aminobutyric acid (GABA) and norepinephrine (NE), will be used to assess the organization of single cells in the rabbit visual cortex, which have thoroughly documented response properties following both normal and abnormal development. The proposed studies will investigate: 1) the role of these transmitter systems in the organization of cells with different receptive field properties, including direction selectivity, orientation selectivity, and selectivity for non-oriented moving and transient stimuli; and 2) the interaction between the response to neurotransmitter application and response to early deprivation which reduces the direction selectivity of cells with orientation selective receptive fields. Thus, the relationship between early experience, neurotransmitter function, and receptive field type will be examined, with special emphasis on direction selectivity. The rabbit visual cortex will be an ideal system for this study because: 1) it contains a greater variety of receptive field types than the cat or primate; and 2) stroboscopic rearing results in a severe reduction of direction selectivity, although a sufficiently large population of cells retains direction selectivity. This will permit a thorough analysis and comparison of cells which: a) retain; or b) lose direction selectivity in response to early deprivation.